<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        .myDiv {
            width: 600px;
            height: 300px;
            margin-top: 100px;
            margin: auto;
            border: black;
            background: black;
        }

        .parentDiv {
            width: 100%;
            padding-top: 100px;
            height: 100%;
        }
    </style>
</head>
<body>
<div class="parentDiv">
    <div class="myDiv">
        <div class="div1"></div>
        <div class="div2"></div>
        <div class="div3"></div>
    </div>
</div>
</body>
</html>
